Communication-based Train Control (CBTC) uses communication media for two-way communication between a train and ground equipment, as a replacement for track circuit for medium achieving train operation control.
Traditional CBTC system concentrates on ground control. A train is registered with a Zone Controller (ZC), under control of the ZC, and take the initiative to report to the ZC. ZC calculates the movement authority (MA) for trains within its managing scope, it realizes interaction of vehicle-ground information through continuous vehicle-ground two-way wireless communication, and tracks operation under target-distance based mobile blocking system. However, traditional CBTC systems need a plurality of devices and have complex interfaces, with huge amount of data exchange. Further, because of presence of delays in the transmission of vehicle-ground transmission, instantaneity of a system is limited, as well as train operation control flexibility and intelligence level.
Due to the shortcomings in a traditional CBTC system and for high safe and efficient operation requirements of a rail transit system, vehicle-vehicle communication based CBTC system rose in response. A vehicle-vehicle communication based CBTC system reduces the number of ground devices, and uses a Vehicle on-board controller (VOBC) as it core. Based on direct communications between trains, a train directly obtains information about vehicles in front or behind it (e.g. train location and speed), it control the speed of the train to prevent collision or rear-end, to make more flexible control of the train so as to improve its the operational efficiency.
However, a vehicle-vehicle communication based CBTC system depends on direct communications between trains, once there is a train without communication equipment or with equipment failure operation in front, the train is unable to learn the operation information that there are other trains in front, causing wrong MA of the train, and therefore resulting in serious danger. In addition, if an obstruction appears in front of the train (e.g., accidental intrusion of objects, or other vehicles stops on the train tracks temporary, or trees or other obstructions on the tracks due to extreme weather), existing vehicle-vehicle communication based CBTC system cannot identify obstacles, so that the train cannot stop in time, causing danger for the train, and even worse, for passengers, an aftermath may be extremely serious.